A multi-option referendum on Scottish independence could be supported by the Scottish Liberal Democrats if it included a question giving the devolved parliament greater powers, the party's new leader has indicated.

Tavish Scott, who was elected the party's new leader today by a hefty margin, said he could try to use the proposed referendum in 2010 to give Scots another option: to strengthen the Scottish parliament's existing powers within the UK, short of independence.

Scott became leader with almost 60% of the party membership's votes, outstripping his two rivals Ross Finnie, a former environment minister, and backbencher Mike Rumbles by more than two votes to one.

The former Lib Dem deputy leader and MSP for Shetland said the result had given him a mandate to lead with "renewed energy and vigour". His party has slumped to fourth place in opinion polls and been repeatedly outflanked and overshadowed by the Scottish Tory party since the Holyrood elections in May 2007.

Scott told senior party figures, including former Scottish leaders Jim Wallace and his immediate predecessor Nicol Stephen, that his first target would be Alex Salmond's Scottish National party administration. Salmond's opponents believe many of his party's policies and pledges are about to falter because of over-spending.

"After 18 months in government, the SNP are riding high. They're popular but here's my prediction: by 2010, they won't be," said Scott. "You can already see the underlying weaknesses that will undo Alex Salmond. What looks like confidence, surefooted and wily today will seem arrogant, misguided and politically dishonest tomorrow. Spin is the hallmark of this government, but spin has a shelf life."

Scott's key task is to rebuild the party's influence and stature at Holyrood, where it shared power with Labour in two successive coalition governments until May last year.

Despite his confident rhetoric, there were heavy hints today that Scott intends to open talks with Salmond on joint policies, particularly a local income tax and perhaps a constitutional referendum. This would allow him to repeat Tory success in delivering new policies since the election.

Salmond's plans for a local income tax have come under sustained attack from business leaders, economists and UK ministers, so Lib Dem support for scrapping the council tax could prove crucial for the SNP's minority government, which holds power on the slimmest of mandates.

Scott's price for that could be holding a multi-option referendum on constitutional reform – a deal that Salmond has previously shown interest in. That could also attract Labour support, since pro-union parties insist the public would vote against full independence.

Asked whether he still believed the Lib Dems should oppose the SNP's independence referendum – his "red line" position before last May's elections, Scott told reporters: "We will see what legislation the SNP comes forward with. I am not intuitively against making sure that people have a choice and opportunity to vote on these things, but I believe it should be for a strengthened Scotland within the UK."

Nick Clegg, the UK party's leader, said he was "delighted" that Scott had been elected. "He will bring energy and enthusiasm to the role, taking the fight to the SNP and Labour right across Scotland," he said.

"Tavish will address the issues that matter most to the people of Scotland, not the narrow-minded squabbles of the nationalists and Labour."

Scott said his leadership would begin tomorrow with a visit to Glenrothes, the Westminster seat left vacant by the death of the Labour MP John MacDougall.

The byelection date has yet to be set, but the Lib Dems said their candidate would be Harry Wills, a local businessman. Labour is due to unveil its candidate next Monday. The byelection is expected to be one of the fiercest fought for some time because it could determine the fate of Gordon Brown's government.

It is the neighbouring seat to Brown's constituency of Kirkcaldy and Cowdenbeath. And while the SNP are already favourites to win, the Lib Dems still hope to repeat their shock result in 2006 when they beat Labour in Dunfermline and West Fife, the once rock solid Labour seat on the other side of Brown's constituency.

• This article was amended on Friday August 29 2008. We have added a paragraph, including a quote from Tavish Scott, to support the assertion that Scott's party may support a multi-option referendum on Scottish independence.